1. Technical Field
An embodiment of the present invention relates to integrated circuit manufacturing, and in particular to a seed layer used to form an interconnect feature in an integrated circuit and/or package substrate.
2. Description of the Related Art
In the fabrication of a die from a wafer, various materials may be deposited on a substrate of the wafer for various purposes. For example, a metal layer may be deposited on a patterned substrate to form interconnect features such as metal lines. The patterned substrate may include trenches within which the metal lines are formed.
The substrate is generally of monocrystaline silicon material, such as silicon dioxide. The trenches may be defined within a silicon based inter-layer dielectric (ILD) material including an abundance of silicon, oxygen, and carbon elements. Additionally, a barrier layer may line the trenches to prevent ion migration from the metal lines to outside of the trenches during operation of the completed integrated circuit. For example, the barrier layer may include tantalum where the metal lines are to be of copper.
In order to ensure adequate adhesion between the materials of the substrate defining the trench as described above, a seed layer may initially be deposited within the trenches. The seed layer generally includes the same metal that is to form the metal lines. Alternatively, an alloy of the metal may be used to form the seed layer.
The seed layer is generally quite thin. For example, the seed layer may be between about 10 angstroms and about 3,000 angstroms in thickness. By way of comparison, the complete metal lines to be formed will fill the trenches and may be between about 0.05 microns and about 20 microns.
The seed layer described above may be carefully deposited, for example, by atomic layer deposition (ALD). In this manner, thin and uniform seed layers are formed that adhere to the silicon or other materials defining the trenches as described above. Additionally, the seed layer may includes material similar to that of the metal lines. For example, the seed layer and the metal lines may both include copper. Therefore, the material to form the remainder of the metal lines adequately conforms with, and adheres to, the seed layer when deposited thereon. The seed layer thus acts as an adhesive interface between the materials of the substrate or barrier layer and the metal lines.
Following deposition of the seed layer, the substrate is generally transferred to a metalization reactor for plating of the material to form the remainder of the metal lines. Unfortunately, as the substrate is transferred, the thin and delicate seed layer is often contaminated. For example, the seed layer, primarily of a metal material, may oxidize as it is exposed to air during the transfer. Additionally, contamination with organic material may occur, for example from the person transferring the substrate. Such contamination may result in defects which affect deposition of the material to form the remainder of the metal lines. In fact, the metal lines formed over such defects are prone to include voids. These voids may prevent transmissions through the metal lines, rendering the metal lines useless. A die formed which includes such defects may fail testing and be discarded.
In order to prevent defects in the seed layer as described above, attempts have been made to clean the seed layer and remove contaminants prior to formation of completed metal lines. For example, the substrate with seed layers may be placed in a cleaning solution and rinsed prior to deposition of the remainder of the metal line material. Unfortunately, surfactants of the cleaning solution are often incompatible with substances used during the deposition of the remainder of the metal line material. As a result, the metal lines are still likely to include voids, rendering them useless. In another attempt to remove contaminants from the seed layer prior to formation of metal lines, the substrate may be heated to temperatures in excess of about 300° C. Unfortunately, this may damage the thin and delicate seed layer. Further, even upon exposure to such temperatures, certain contaminants as described above are likely to remain on the seed layer.